Frozen smoke.

Aerogel, also know as frozen smoke, is the world’s lowest density solid, clocking in at 96% air. If you hold a small piece in your hand, it’s practically impossible to either see or feel, but if you poke it, it’s like styrofoam. It supports up to 4,000 times its own weight and can withstand a direct blast from two pounds of dynamite. It’s also the best insulator in existence. via dvice.com